Fix LoadExactInterfaceMap for sub-interfaces with complex type arguments under special marker parents#124684
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davidwrighton merged 4 commits intodotnet:mainfrom Feb 25, 2026
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…nts under special marker parents When pNewIntfMT is a special marker type and its sub-interface has an exact instantiation containing complex type arguments (e.g. IList(Of T) rather than bare T), the previous code would fall through to case 4 which checked EligibleForSpecialMarkerTypeUsage against pMT. This could incorrectly treat the sub-interface as an exact match when it still contains unresolved generic variables. Split old case 4 into three new cases: - Case 4: pNewIntfMT is a special marker type and the sub-interface's instantiation is eligible for special marker usage relative to pNewIntfMT (e.g. ILayer1(Of T) where T matches). Insert the marker. - Case 5: pNewIntfMT is a special marker type but the sub-interface has generic variables that don't match (e.g. ILayer1(Of IList(Of T))). Trigger retry with exact interfaces since full substitution is needed. - Case 6: The sub-interface is fully concrete or pNewIntfMT is not a special marker. Fall through to the existing pMT-based eligibility check. Add regression tests covering all 8 combinations of pre-loading the 3 interface layers. Co-authored-by: Copilot <[email protected]>
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Pull request overview
Fixes CoreCLR interface-map exact-loading for the case where a special marker parent interface contains a sub-interface entry that is an exact instantiation with more complex type arguments (e.g., IList<T>), preventing incorrect eligibility checks and ensuring the algorithm falls back to the exact-interface retry path when deep substitution would be required.
Changes:
- Split the prior “exact instantiation” handling in
LoadExactInterfaceMapinto additional sub-cases to correctly handle special-marker parents and open generic variables. - Add a VB regression test suite (with 8 preload-order combinations) to exercise the special marker interface map logic and validate the fix.
Reviewed changes
Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.
| File | Description |
|---|---|
| src/coreclr/vm/methodtablebuilder.cpp | Refines LoadExactInterfaceMap handling for exact sub-interfaces under special marker parents, including a controlled fallback path. |
| src/tests/Loader/classloader/regressions/GitHub_124369/GitHub_124369.vb | Adds VB regression coverage for the reported failure mode across multiple preload orderings and interface layering shapes. |
| src/tests/Loader/classloader/regressions/GitHub_124369/GitHub_124369.vbproj | Adds the test project definition for the new VB regression test. |
This was referenced Feb 21, 2026
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Co-authored-by: Copilot <[email protected]>
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/azp run runtime-coreclr outerloop |
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Azure Pipelines successfully started running 1 pipeline(s). |
jkotas
approved these changes
Feb 24, 2026
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/ba-g Only failing case is #122345 which the build analysis tools didn't find for some reason. |
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/backport to release/10.0 |
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Started backporting to |
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Summary
When
pNewIntfMTis a special marker type and its sub-interface in the interface map has an exact instantiation containing complex type arguments (e.g.IList<T>rather than bareT), the previous code inLoadExactInterfaceMapwould incorrectly fall through to the old case 4 logic. This checkedEligibleForSpecialMarkerTypeUsageagainstpMTrather thanpNewIntfMT, which could treat a sub-interface still containing unresolved generic variables as either eligible for special marker substitution or as an exact match — both incorrect.Fix
The old case 4 (exact instantiation) is split into three cases to correctly handle the situation where
pNewIntfMTis itself a special marker type:pNewIntfMT(e.g.ILayer1<T>whereTmatchespNewIntfMT's type parameter). Insert the special marker type.pNewIntfMT's type parameter (e.g.ILayer1<IList<T>>). Since resolving this requires a full deep substitution, and this is a rare scenario, we fall back to the retry-with-exact-interfaces pathway which setsMayHaveOpenInterfacesInInterfaceMapand disables the special marker optimization for this type.pNewIntfMTis not a special marker type. Falls through to the existingpMT-based eligibility check, which is correct in these situations.A regression test is added covering all 8 combinations of pre-loading the 3 interface layers' generic type definitions before constructing the concrete class, to exercise the various orderings that lead to different code paths through the special marker type logic.
Fixes #124369